Musnad Ahmad 5:235

Abdullah narrated to us, Abu Ubaydah bin Fudayl bin Iyad narrated to us—and he said to me: "It is my name and my kunya"—Malik bin Su'ayr, meaning Ibn al-Khums, narrated to us, Furat bin Ahnaf narrated to us, my father narrated to us, from Rib'i bin Hirash, that Ali bin Abi Talib stood as a preacher in al-Rahbah. He praised Allah and extolled Him, then he said what Allah willed for him to say. Then he called for a pitcher of water, rinsed his mouth with it, wiped [parts of his body], and drank the remainder of his pitcher while he was standing. Then he said: "It has reached me that a man among you dislikes to drink while he is standing, but this is the ablution of one who has not broken his state of purity, and I saw the Messenger of Allah, may Allah bless him and grant him peace, do exactly like this."